The journey from Krabi (Ao Nang), Thailand to Penang, Malaysia is easily done by minivan.
All travel agents in Krabi sell tickets, and after asking around they all seemed to be for 900 baht, some as high as 1,200 baht. There are two companies that run this route, with a 6am pickup (Ao Nang) and a 9 or 10am pickup. The 6am departure arrives in Penang at 4pm, the other at 7 or 8pm. I opted for the 6am departure so i still had some daylight when I arrived. I tried to book the ticket two days in advance, but they didn’t have any bookings for the 6am departure, so hadn’t confirmed if it would run yet. They only run with a minimum of two people. I waited another day and checked again and managed to get a ticket, otherwise I would have had to get on the 10am departure.
The minivan was actually full, with four ‘western’ tourists and 9 Malaysian tourists. We arrived at Hat Yai at 11.30am, and dropped the Malaysians off at various places, then the four of us had to wait one hour until another minivan arrived to take us to Penang.
We didn’t get to the border until about 2pm (Thai time). And then it took almost one hour to get through Thai immigration. At Malaysian immigration, it only took 15 minutes, but we had to wait over one hour for two or three people from our van to get through. Finally at 5pm Malaysian time we left immigration and headed south, taking some insane detour, arriving in Georgetown, Penang at almost 8pm.
*I wanted to get the train to Penang from Hat Yai in Thailand, but the ‘through’ trains have recently been cancelled and this now requires a changeover at Pedang Besar on the border. This would also need a 450 baht minivan to Hat Yai (and possibly a night in Hat Yai) so for simplicity I decided against the train. Seat61 does have some fairly up-to-date info on the train option though.